Enzymes are proteins which catalyze a wide variety of chemical reactions, many of great commercial importance. Enzymes are generally classified according to the type of reaction which they catalyze, e.g., hydrolases are enzymes that catalyze the addition of the elements of water across the bond that is cleaved, e.q., an ester or peptide linkage. Commercially-important hydrolases include proteases which are employed in laundry detergents, polysaccharidases which control slime in industrial process waters, and lipases which are employed to transesterify fats and oils. Cellulases and ligninolases can be employed in wood fiber production and bleaching.
The hydrophilicity, or high water-solubility, of many of these enzymes often reduces their utility in hydrophobic (lipophilic) media and their reactivity with hydrophobic substrates. The biocatalytic reaction is inefficient due to phase separation between the two reactants. Either the enzyme is introduced into an aqueous phase in which the hydrophobic substrate is insoluble, or neither the enzyme nor the hydrophilic substrate can dissolve or disperse in the hydrophobic medium. For example, the removal of oily or fatty soils from food processing equipment cannot be readily accomplished with aqueous lipase solutions due to the lack of affinity of the enzyme for the hydrophobic residues. Furthermore, even in the presence of stabilizers, the activity of free enzymes often decreases rapidly in aqueous media.
One attempt to partly circumvent these problems involves contacting aqueous dispersions or solutions of the target substrate with enzymes which have been immobilized by physical adsorption or covalent bonding to water-insoluble carriers such as cellulose fibers or silica beads. Enzymes have also been immobilized by entrapping them in polymeric matrices. See K. Yokozeki et al., European J. Appl. Microbiol. Biotechnol., 14, 1, (1982). Circulation of a stream of the substrate or a dispersion thereof through a zone containing the immobilized enzyme can reduce losses due to the addition of free enzymes to a process water stream. However, immobilization or entrapment of enzymes can reduce their activity. Furthermore, the substrate matrix can further reduce the efficiency of enzyme-substrate contact.
Therefore, a need exists for a method to selectively decrease the water-solubility of hydrophilic enzymes such as hydrolases, and thereby to increase the efficiency of enzymatic interaction with hydrophobic substrates in aqueous media.